The present invention relates to a method and means to estimate the degree of compaction obtained when compacting a bed with the aid of a compacting machine of a certain kind. The method and the means are meant for such compacting machines having a compacting drum which is rotatably suspended about its axis and operates according to the principle described in European Pat. No. 0053598. The principle is that a torque is applied to the compacting drum about its axis. The torque changes direction between clockwise and counter-clockwise rotation with a certain frequency of reversal.
There has been a long time desire for a simple, cheap and dependable continuous meter for measuring the degree of compaction which is attained during the compaction of a bed. In recent years there have been several different meters designed to meet this desire, i.e., for conventional vibrating rollers. Examples are mentioned of such designs in U.S. Pat. No. 4,103,554 and European Pat. No. 0,065,544. The compacting machines for which the present invention is directed to, function in a principally different manner then ordinary vibrating rollers. Compaction meters, e.g. according to U.S. Pat. No. 4,103,554 and European Pat. No. 0065544 can therefore not be used for the type of compacting machine contemplated by the present invention. There is no generally known method or means for estimation of the compaction degree attained by the type of compaction machine contemplated by the present invention. The present invention utilizes a method and a means which continuously estimates the attained degree of compaction during compaction work with precisely this type of compacting machine. The meter is located on the roller.
The present invention is based on sensing the motion of the compacting drum when the compacting machine is moved forward and backwards across the top of the bed and the alternating torque being applied to the compacting drum about its axis.
The present invention is based on the knowledge that the acceleration of the drum about its center or axis in a direction perpendicular to the drum axis and substantially parallel to the bed is related to the degree of compaction of the bed. Therefore, a value is generated in a method according to the invention which represents this acceleration. A device according to the invention, is also needed for generation of such a quantity.
The present invention is also based on the knowledge that the acceleration amplitude need not be directly related to the degree of compaction since the compacting drum can also slide against the bed. The present invention is based on the knowledge that an estimation of the attained degree of compaction can be made with the aid of the acceleration at certain points of time or when certain time intervals during the drum mantle remains in contact with the bed, but, contrary to the application of the alternating torque, not slip appreciably against the bed. In the method, according to the present invention, at least one such time interval or point of time is determined with the aid of the generated value. Furthermore, the frequency of reversal or its corresponding period or a parameter which is a function of these conditions is determined with the aid of the time plot of the measured acceleration during those time intervals described above and the frequency of reversal or the period. Means, according the present invention, embodies a transducer for sensing the motion of the drum and a processor for calculating the obtained degree of compaction.